Conventionally, as inkjet inks excellent in water resistance, there are those obtained by dispersing or dissolving an oil-soluble dye in a high boiling point solvent and those obtained by dissolving an oil-soluble dye in a volatile solvent.
As to colorants that have been used, dyes are inferior to pigments in various kinds of resistance such as light resistance. However, it is generally not easy to disperse a pigment stably in an organic solvent, and it is usually difficult to secure a stable dispersibility and discharging property.
As to ink solvents, an ink using a high boiling point solvent shows no solvent volatilization on a non-absorbing type recording medium, and manifests difficult drying through the evaporation of solvents, hence impossibility of printing onto non-absorbing type substrates. On the other hand, in the case of an ink using a volatile organic solvent, it is possible to form excellent prints even on a non-absorbing substrate by the adhesive property of a resin used and evaporation of solvents. However, since a volatile solvent is the main component of the ink, drying by volatilization of a solvent is very quick on the nozzle surface of a head, and frequent maintenance is required. Further, as inks are essentially required to be re-soluble in solvents, resistance to solvents is not sufficiently obtained in some cases.
While there have been such various problems, there is also a utilization of inks of the type which prevents drying in a head by using non-volatile monomers and completes hardening by providing active energy rays. Such inks are disclosed, for example, in Japanese Patent Application Laid-Open (JP-A) Nos. 62-64874 and 58-32674. These inks are typically used in printers of continuous type, and particularly, inks having a viscosity of 3 to 5 mPa·s are generally used. Since this type of printer discharges inks continuously, a plurality of volatile solvents can be used together and in large amounts, and control of viscosity of the inks and impartment of volatility are relatively easy.
On the other hand, in an on demand mode printer using a piezo element, use of a large amount of volatile solvents increases frequency of maintenance and tends to cause a problem of dissolution and swelling of ink contact materials in a printer Also, volatile solvents are restrained more strictly as a hazardous material defined by the fire protection law. In the case of an on demand type printer using a piezo element, an ink having a smaller amount of volatile solvents is thus required. However, materials used in an active energy beam curable ink have been had relatively high viscosity. Inks having so low viscosity as to enable discharge also in a conventional type printer, an excellent curing property, and excellent stability, have not been obtained until now.
One object of the present invention is to provide an active energy beam curable inkjet ink having low viscosity, excellent photo-polymerizability, excellent curing property, and good stability.
Another object of the present invention is to provide an active energy beam curable inkjet ink causing no dissolution and swelling of ink contact materials in a printer, and showing excellent discharge stability from nozzles, excellent adherence to a recording medium, and excellent solvent resistance and water resistance.